Signal Generating Circuit, Optical Signal Transmitting Apparatus, Signal Receiving Circuit, Method for Establishing Optical Signal Synchronization, and Optical Signal Synchronization System

1. A signal receiving circuit in optical communication, the signal receiving circuit comprising: a photoelectric conversion circuit that converts an input optical signal into an electrical signal; an analog/digital conversion circuit that converts the electrical signal converted by the photoelectric conversion circuit into a digital signal; a Fourier transform circuit that performs a discrete Fourier transform on the digital signal converted by the analog/digital conversion circuit; a specific frequency band signal detecting circuit that detects a position in a frequency domain of a specific frequency band signal having power concentrated on two or more specific frequencies from a signal obtained by the discrete Fourier transform; a reception signal property estimating circuit that estimates at least one of a frequency offset and a clock offset from the position of the specific frequency band signal detected by the specific frequency band signal detecting circuit; and a specific frequency band signal power storage circuit, wherein the Fourier transform circuit performs the discrete Fourier transform at an interval smaller than or equal to the smaller of a length of the specific frequency band signal and a Fourier transform length, wherein the specific frequency band signal detecting circuit detects, for two or more frequencies, specific frequency band signal power values that are powers or amplitudes of the specific frequency band signal in a signal in a frequency domain subjected to the discrete Fourier transform by the Fourier transform circuit, and stores two or more values of an increasing value, a peak value, a decreasing value, and a minimum value among the detected specific frequency band signal power values, an individual arrival time difference calculated from the specific frequency band signal power values, or a coefficient that is calculated from the specific frequency band signal power values and is used in an calculation equation of the individual arrival time difference, in the specific frequency band signal power storage circuit, and wherein the reception signal property estimating circuit estimates an arrival time difference between specific frequency band signals corresponding to two or more frequency bands using the two or more values of the increasing value, the peak value, the decreasing value, and the minimum value among the detected specific frequency band signal power values, the individual arrival time difference calculated from the specific frequency band signal power values, or the coefficient used in the calculation equation of the individual arrival time difference, which are stored in the specific frequency band signal power storage circuit, and estimates a chromatic dispersion amount of an optical communication path from the estimated arrival time difference.

2. The signal receiving circuit according to claim 1 , wherein the specific frequency band signal detecting circuit shifts frequencies for which the specific frequency band signal power values are to be calculated, using information on a frequency offset estimated by the reception signal property estimating circuit or externally input frequency offset information when detecting the specific frequency band signal power values, which are the powers or the amplitudes of the specific frequency band signal in the signal in the frequency domain subjected to the discrete Fourier transform.

3. A signal receiving circuit in optical communication, the signal receiving circuit comprising: a photoelectric conversion circuit that converts an input optical signal into an electrical signal; an analog/digital conversion circuit that converts the electrical signal converted by the photoelectric conversion circuit into a digital signal; a Fourier transform circuit that performs a discrete Fourier transform on the digital signal converted by the analog/digital conversion circuit; a specific frequency band signal detecting circuit that detects a position in a frequency domain of a specific frequency band signal having power concentrated on two or more specific frequencies from a signal obtained by the discrete Fourier transform; a reception signal property estimating circuit that estimates at least one of a frequency offset and a clock offset from the position of the specific frequency band signal detected by the specific frequency band signal detecting circuit; a specific frequency band signal power storage circuit; and a chromatic dispersion compensating circuit that applies an inverse property of chromatic dispersion to the digital signal converted by the analog/digital conversion circuit based on an estimated value of a chromatic dispersion amount estimated by the reception signal property estimating circuit, wherein the reception signal property estimating circuit estimates the chromatic dispersion amount of an optical communication path from an offset in timing of appearance of the power of the specific frequency band signal, an offset in timing of disappearance of the power, or both the offset in timing of the appearance of the power and the offset in timing of the disappearance of the power, wherein the Fourier transform circuit performs the discrete Fourier transform on the digital signal to which the inverse property of the chromatic dispersion has been applied, at an interval smaller than or equal to the smaller of a length of the specific frequency band signal and a Fourier transform length, wherein the specific frequency band signal detecting circuit detects specific frequency band signal power values that are powers or amplitudes of the specific frequency band signal in a signal in a frequency domain subjected to the discrete Fourier transform by the Fourier transform circuit, and stores two or more values of an increasing value, a peak value, a decreasing value, and a minimum value among the detected specific frequency band signal power values, an individual arrival time difference calculated from the specific frequency band signal power values, or a coefficient that is calculated from the specific frequency band signal power values and is used in a calculation equation of the individual arrival time difference, in the specific frequency band signal power storage circuit, and wherein the reception signal property estimating circuit estimates an arrival time difference of specific frequency band signals corresponding to two or more frequency bands using the two or more values of the increasing value, the peak value, the decreasing value, and the minimum value among the detected specific frequency band signal power values, the individual arrival time difference calculated from the specific frequency band signal power values, or the coefficient used in the calculation equation of the individual arrival time difference, which are stored in the specific frequency band signal power storage circuit, estimates a chromatic dispersion amount of an optical communication path from the estimated arrival time difference, and outputs the estimated chromatic dispersion amount to the chromatic dispersion compensating circuit.

4. The signal receiving circuit according to claim 3 , wherein the chromatic dispersion compensating circuit deletes at least part of content stored in the specific frequency band signal power storage circuit when changing a coefficient for chromatic dispersion compensation, and the reception signal property estimating circuit stores a chromatic dispersion amount of the optical communication path estimated for a new signal sequence in the specific frequency band signal power storage circuit.

5. The signal receiving circuit according to claim 3 , wherein the chromatic dispersion compensating circuit applies the inverse property of the chromatic dispersion to the digital signal converted by the analog/digital conversion circuit based on the estimated value of the chromatic dispersion amount estimated by the reception signal property estimating circuit, and notifies the Fourier transform circuit of detection of the specific frequency band signal when the specific frequency band signal is detected, and the Fourier transform circuit performs the discrete Fourier transform at the interval smaller than or equal to the smaller of the length of the specific frequency band signal and the Fourier transform length, and outputs the signal subjected to the discrete Fourier transform to the specific frequency band signal detecting circuit when the detection of the specific frequency band signal is notified.

6. The signal receiving circuit according to claim 3 , wherein the chromatic dispersion compensating circuit applies the inverse property of the chromatic dispersion to the digital signal converted by the analog/digital conversion circuit based on the estimated value of the chromatic dispersion amount estimated by the reception signal property estimating circuit, and outputs a signal including the specific frequency band signal to the Fourier transform circuit, the Fourier transform circuit performs the discrete Fourier transform on the signal including the specific frequency band signal output from the chromatic dispersion compensating circuit at an interval smaller than or equal to the smaller of the length of the specific frequency band signal and the Fourier transform length, and outputs the signal subjected to the discrete Fourier transform to the specific frequency band signal detecting circuit when the specific frequency band signal is detected, and the specific frequency band signal detecting circuit acquires two or more values of the increasing value, the peak value, the decreasing value, and the minimum value among the specific frequency band signal power values from the signal subjected to the discrete Fourier transform output from the Fourier transform circuit, and stores the two or more acquired values in the specific frequency band signal power storage circuit.

7. The signal receiving circuit according to claim 3 , wherein the specific frequency band signal detecting circuit shifts frequencies for which the specific frequency band signal power values are to be calculated, using information on a frequency offset estimated by the reception signal property estimating circuit or externally input frequency offset information when detecting the specific frequency band signal power values, which are the powers or the amplitudes of the specific frequency band signal in the signal in the frequency domain subjected to the discrete Fourier transform.